High temperature alloy



Oct.;13, 1959 J. A. NELSON 2,908,565

HIGH TEMPERATURE ALLOY Filed Aug. 29,1956

7. COPPER N 0 Q l 2 3 4 5 6 7 I 8 9 [0 II I2 l3 l4 l5 COBALT INVENTOR.Jaw/y #52500 United States Patent HIGH TEMPERATURE ALLOY John A. Nelson,Braeburn,Pa., assignor to Continental Copper & Steel Industries, Inc.(Braeburn Alloy Steel Division), New York, N.Y.,' a corporation ofDelaware Application August 29, 1956, Serial No. 610,042

6 Claims. (Cl. 75-125) The present invention relates to alloys for hightemperature application and it particularly relates to free machiningprecipitation hardening alloys. The present invention will'beparticularly described in regard to novel free machining cobalt-copperhardening alloys for high temperature applications which are involved inconnec: tion with die casting dies, plastic molds, extrusion dies, andforging dies. r

-It,' has been found quitediflicult .to providemost'satisfactory alloyswhich maybe made at moderate costs and at commercial selling priceswhich will provide great resistance to softening under heat, whileat-the same time providing ready machinability, even, though having highhardness values, and it isfamo-n'g the primaryobjects -of the presentinvention to provide die steel alloys of moderate costs which willcombine vhigh machinability, even though very hard, with high resistanceto softening under heat.

It isa further object of the present invention to pro vide novelcobalt-copper low carbon alloy steels which have a particularapplication for hot work applications and which will be highly resistantto heat checking, which will;be subject to aminimum distortion on heattreatment, which will be abrasion resistant,- which will have a minimumtendency to stick or solder to thework, which may be polished tojhighmirror finish,- and, which will be highly resistant bothto corrosion andheat checking.

A particular object of the present invention is to provide novel, freemachining, precipitation hardening alloy steels for high temperatureapplications which may be most desirability utilized for dies for suchhot work applications as die casting, extrusions, forgings, and mouldedplastics Stillfurther objects and advantages will appear in the moredetailed description set forth below, it being understood, however, thatthis more detailed descriptionis given byway. of illustration andexplanation only and not-by way of limitation, since various changestherein may be made by those skilled in the art without departing fromthe scope and spirit of the present invention.

In accomplishing the above objectsit has been found that at least 2 /2of cobalt and desirably about 4 to 6% cobalt is eflfective. Copper inamounts ranging from about A to /2 of the cobalt content is alsoeffective in contributing to precipitation hardening and free machiningqualities.

While the addition of copper is efiective and is included in thepreferred analysis, desirable properties for some applications can beobtained with cobalt alone in the absence of copper.

' In the preferred alloy the carbon content is low, desirably less thanabout .15 Chromium and molybdenum is added with or without tungsten andnickel.

The essential feature of the present invention is to provide novel, freemachining, precipitation hardeningfalloys ICC peratures up to about 1500F.,Machining is usually done after suitable solution heat treatment.Upon age hardening, hardnesses up to about 50 Rockwell C are obtainedwith. a negligible or a minimum amount of distortion from heattreatment.

It is found that the alloy has the desirable proper-ties which are mosteffective when there is a substantial absence in the alloy of sulphur,lead, selenium, tellurium or silver, and when there isalso-substantially absent, or in very low amounts, carbon, manganese,silicon and "vanadium inquantities less than 0.5% and desirablynot'exceeding 0.2%, and when any nickelthat maybe present is.in amountsless than 1% and desirably in theneighborhood of 0.5% or less. 1 Thedrawing is a diagrammatic chart disclosing the preferred range and thewidest specified range in cobalt and copper to obtain the desiredeffect.

These alloys in addition have excellent polishability and freedom fromheat checking in use. V

The most important feature of thepresent invention resides in thediscovery-that cobalt above about 2%% .and' less than about 8%, andpreferably with copper in minor proportion will give these unusual anddesirable properties. 7

The copper should preferably be added in amounts at least in excess ofits solid solubility in the steel.

Cooper in amounts less than about /z% is not most effective in impartingfree machining characteristics. Above 4 or 5%, hot working diflicultiesare encountered. The preferred range of copper in the alloy should befrom /2% to 2%%.

With the addition ofl to 3% of copper, cobalt in the preferredrange 4 to6% will result in hardnesses up to about 5'0 Rockwell C after suitablesolution and aging treatments.

Nickel may be added up to about 1% to enhanceage a hardening and toimprove forgea'bility. The nickel conplications. Said alloys areparticularly useful at temtent should be about half of the coppercontent for max imum eifectiveness in avoiding cracking on forging orother hot working operations.

For maximum age hardening characteristics. thelcarbon should, be keptlow,'preferably less than about'.15%.f

With over'.30% carbon substantially lower hardness will result on agehardening. t

,Cobalt should be added in amounts inexcess of about 2 /z% and,preferably in the range of about 4 to 6%.

, Copper in amounts less than /z% is relatively inefiective and copperin the preferred analysis is added in amounts ranging from about 1 /2 to2%%. The ratio of copper to cobalt should be in the range of 1:5 to 1:2.

Molybdenum with or without tungsten constitutes an important addition.Molybdenum in excess of about 3% results in alloy steels which are lessmachinable and the molybdenum content therefore should be lessthan about3 /2%. Also, if tungsten is included it should vdesirably be less thanthe molybdenum content. Suitable results areobtained with the ratio ofmolybdenum 'to tungsten substantially in the ratio of 5:4 or 4:3.

Chromium contributesto age hardeningand may-be present up to about 6%.'Best machining characteristics are achieved where the chromium contentexceeds the molybdenum content and preferably the excess of chromiumovermolybdenum should be in the ratio of 5:4 or greater.

Vanadium should be kept relatively low, less than 1%. Likewise manganeseand silicon are kept relatively low, not over about 1%. Vanadium,manganese, and

silicon are not of critical importance and may be present in somewhatlarger amounts than the preferred range cited without detracting fromthe advantageous properties of the alloy.

Phosphorusand sulphur do not normally exceed about I Patented Oct. 13,1959 .03% each, and in this range their effect is minor. Aluminum may beadded in small amounts up to about 5% Aluminum acts as a deoxidizer inmelting and also contributes somewhat to age hardening. A

Example 1 Preferred Range Broad Range Less than about .15%. Less thanabout .60% Less than about 60%-.

Below about .30%. Below about 1.00%. Below about 1.00%.

About 2 to 4% Below about 6%. About 1 to 2% Below about 3%. About .75 to2.75% Below about 5%. Less than about .50% Below about 1%. About 4 to 6%About 2% to 8%.

Below about 2%.

About .50 About 1% to 2%% About to 4%.

Balance substantially iron. I

All'percentages by weight. p

The above alloy steels have excellent machinability at high'hardness andretention of hardness at elevated temperatures. They may. also includeother" ferrite forming alloying elements such as titanium or columbiumin restricted amounts without detrimentally afiecting the machinability.

As set forth above, the molybdenum should be below' but desirably itshould be keptless than Il /2% sincev if the percentage is in excess of3 /2%, the steel is less machinable. The preferred .range of molybdenumis .75 to 2.75%. I

Preferably the cobalt should be present in a minimum percentage of 2%but in most instances the minimum percentageshould preferably be 2 /2%of cobalt.

On the other hand, the copper, nickel and tungsten should be present ina maximum percentage of 4 /2 3 and 5% respectively, with the preferredmaximum of each of these elements not exceeding in the preferred alloy4%, 2% and 3%.

In respect to the combined cobalt and copper, it should at all 'times bein the range of 2 to 15%, although preferably it'should be in the rangeof 2 /2 to 12%.

Example II Asa specific steel alloy melted and tested according to thepresent'invention, the following is cited:

Balance substantially iron.

- Steels conforming to these proportions possess characteristicswhich-are outstanding for hot work die steels for die casting,extrusion, metal forming and other high temperature applications. Thesesteels are precipitation hardening and may be furnished in a variety of-conditions. Such steels can'be solution treated at tempera- 4 turesabout 1850 F. followed by air cooling to a hardness in the range ofabout 40/45 Rockwell C. In this condition the steels are very readilymachinable.

After machining the die may be aged or tempered at about between 1000 F.and 1050 F. for a Rockwell C hardness of about 50. The distortion onheat treating is negligible and is much less than is found on steelswhich harden by the formation of martensite from austenite.

Example III As a third example the following percentages by weight maybe included:

These steels machine very well in the as forged condition at about 41 to44 Rockwell C, following which they may be aged or tempered to desiredhardnesses up to about 50 Rockwell C.

Another variation in heat treating consists in hardening andv temperingto about 41 to 44 Rockwell C after which the impression may be machinedby the consumer and then the die is used without further tempering.

Secondary hardening or aging takes place by the heat imparted to the diesurfaces from contact with hot metal in use. This develops hard surfaceat about 50 Rockwell C and a softer core to withstand shock at about 43Rockwell C.

Side rake angle degrees 8 Back rake angle do 5 Side relief angle do 6End relief'angle do 8 End cutting edge angle do 12 Nose radium Iinches..- 5

Surface R.p.m Depth of Cut Speed, Result .Imin.

212 .050 of an inch 176 Cut without failure. 328 .010 of an inch 257 Do.328 .025 of an inch"... 215 Do.

As a further example of the excellent machinability of this steel at 42Rockwell C, drill tests were conducted using a %4-ll'l0h diameter drillat 500 r.p.m. The material drilled very easily with very littlegeneration of heat.

The present invention dilfers from high cobalt, low carbon machinablesteels disclosed in US. Patent No. 2,598,714, issued to John A. Nelsonand Charles W. Sch'uck, in the provision of copper in combination withcobalt.

Whereas the low carbon steels disclosed in US. Patent No. 2,598,714contain about 16 to 30% cobalt together with. Smaller amounts ofchromium, molybdenum, vanadi- 5 am, and tungsten and may be hardened upto a maximum of about 62 Rockell C, the alloy steels of the presentinvention are used at substantially lower hardnesses in the range up toabout 5 Rockwell C and have a considerably lower cobalt content.

It will be noted that the present invention achieves free machiningproperties without sulphur, lead, selenium, tell urium or silver, all ofwhich have been proven unsatisfactory for many purposes.

For example, sulphur makes the steel hot short increasing greatly thedifliculties on hot working. Sulphur also adversely affects thetransverse impact strength and contributes to pitting and surfaceblemishes on die cavities which are highly polished such as plasticmolds or die casting dies.

Lead :gives rise to toxic fumes and because of its high specific gravityas compared with steel, the lead tends to segregate and give uneven andununiform steels, particularly in large sections.

Selenium and tellurium also give toxic fumes. Silver has never provedpracticable for free machining characteristics.

Surprisingly by use of cobalt, copper combinations, a novel steelcomposition is provided which has the un usual characteristics of a freemachining precipitation hardening alloy which is substantially free fromdistortion on heat treating. It may be agedor tempered at 1050 F. aftersolution treating to give a hardness of about Rockwell C 50.

As many changes could be made in the above high temperature alloys, andmany widely difierent embodiments of this invention could be madewithout depart ment from the scope of the claims, it is intended thatall matter contained in the above description shall be interpreted asillustrative and not in a limiting sense.

Having now particularly described and ascertained the nature of theinvention, and in what manner the same is to be performed, what isclaimed is:

1. A free machining precipitationhardening cobaltcopper alloy die steel,and capable of being polished to high mirror finish and capable of beingaged and tempered at about or above 1,000 F. to a Rockwell C hardness ofabout 50, composed principally of iron alloyed with cobalt, nickel,carbon and copper, the cobalt and copper together ranging from 2 to 15%and the cobalt being present in about three times the quantity of thecopper, nickel being included in amount ranging up to about one-half thepercentage of the copper, balance principally iron.

2. A free machining precipitation hardening cobaltcopper alloy diesteel, and capable of being polished to high mirror finish and capableof being aged and tempered at about or above 1,000 F. to a Rockwell Chardness of about 50, composed particularly of iron not over about .25carbon, about 1 to 6% chromium, not over 3% tungsten, not over 5%molybdenum, about 2 to 8% cobalt, about /2 to 4%% copper and not over 3%nickel, the copper being present in an amount approximately one-third ofthe cobalt content and the ratio of molybdenum to tungsten being about 5:4, balance principally iron.

3. A tree machining precipitation hardening cobalthigh mirror finish andcapable of being aged and tem-,

pered at about or above 1,000 F. to a Rockwell C hardness of about 50,composed particularly of iron and less than about .25% carbon, about 1to 6% chromium, about 2 to 8% cobalt, less than 4% tungsten, less than5% molybdenum and copper in an amount in excess of its solid solubilityin said steel but not over about 4 /2% and the remainder iron, thecopper being present in an amount approximately one-third of the cobaltcontent and the ratio of molybdenum to tungsten being about 5:4.

5. A free machining precipitation hardening cobaltcopper alloy diesteel, and capable of being polished to high mirror finish and capableof being aged and tempered at about or above 1,000" F. to a Rockwell Chardness of about 50, composed particularly of iron and not over about.25 carbon, about 1 to 6% chromium, about 2 to 8% cobalt, about /2 to 4/2 copper, l to 5% tungsten, 1 to 5% molybdenum, in which the ratio ofmolybdenum to tungsten is 5 :4, and copper in an amount approximatelyone-third of the cobalt content, balance principally iron.

6. A free machining, precipitation hardening cobaltcopper alloy diesteel capable of being polished to a high mirror finish and capable ofbeing aged and tempered at about or above 1000 F. to a Rockwell Chardness of about 50, comprising principally iron, carbon, cobalt andnickel in the following proportions by weight:

Cobalt, 2 /2 to 6%.

Copper, A to of the cobalt content Carbon, less than about 0.15%

Chromium, up to 6% Vanadium, less than 1% Manganese, less than 1%Silicon, less than 1% Molybdenum, less than 3 .6%

Tungsten in a ratio of between 5:4 and 4:3 to the molybdenum Balanceprincipally iron.

References Cited in the file of this patent UNITED STATES PATENTS2,197,098 Davis et al. Apr. 16, 1940 2,565,264 Payson Au 21, 19512,697,035 Clarke D c. 14, 1954 FOREIGN PATENTS 677,967 France 2. Dec.19, 1929 OTHER REFERENCES Gregg et al.: Alloys of Iron and Copper, pages97 and 160, 1934. Published by McGraw-Hill, New York, NY.

1. A FREE MACHINING PRECIPITATION HARDENING COBALTCOPPER ALLOY DIESTEEL, AND CAPABLE OF BEING POLISHED TO HIGH MIRROR FINISH AND CAPABLEOF BEING AGED AND TEMPERED AT ABOUT OR HAVE 1,000* F. TO A ROCKWELL CHARDNESS OF ABOUT 50, COMPOSED PRINCIPALLY OF IRON ALLOYED WITH COBALT,NICKEL, CARBON AND COPPER, THE COBALT AND COPPER TOGETHER RANGING FROM 2TO 15% AND THE COBALT BEING PRESENT IN ABOUT THREE TIMES THE QUANTITY OFTHE COPPER, NICKEL BEING INCLUDED IN AMOUNT RANGING UP TO ABOUT ONE-HALFTHE PERCENTAGE OF THE COPPER, BALANCE PRINCIPALLY IRON.